1. Field of the Invention
The present invention relates to a dye developer useful for light-sensitive materials capable of forming color images by the diffusion transfer process and, more particularly, it relates to a precursor of a yellow dye developer, which is hydrolyzed in alkaline solution to form a yellow color dye.
2. Description of the Prior Art
A diffusion transfer process utilizing a dye developer is well known in the photographic art (for example, as disclosed in U.S. Pat. Nos. 3,201,384 and 3,246,985).
The dye developer, as noted in U.S. Pat. Nos. 3,201,384 and 3,246,985, is a compound which contains, in the same molecule, both a group capable of developing a silver halide and a chromophoric system of a dye, and which can be immobilized in the amount corresponding to the amount of developed silver halide and of which the residual amount can be transferred to an image-receiving layer to form transferred dye images.
When a hydrophilic colloid layer (e.g., a gelatin layer) containing the dye developer is provided at the photoexposure side to the light-sensitive emulsion layer having substantial spectral sensitivity in the spectral region of the dye (developer) or the dye developer is included in the light-sensitive emulsion layer, the light-sensitive emulsion is seemingly desensitized by the light-absorption of the dye developer. In order to prevent the desensitization of the silver halide emulsion, a proposal has been made that the dye developer be chemically modified and converted into a compound whose spectral absorption region has been relocated at substantially shorter wavelengths for at least the time interval necessary to accomplish photoexposure of the light-sensitive emulsion and which, however, reacts with a processing solution during processing to subject the compound to a restoration of the original absorption characteristics of the dye developer. Such a dye developer is defined as a "temporarily shifted dye developer" in the specification.
However, since a temporarily shifted yellow dye developer is processed in an alkali processing solution to produce a carboxyl group, simultaneously, the quinone form of the dye developer produced in the exposed portions as a result of is development is incompletely immobilized, and therefore, unavoidably an undesirable amount of the dye is transferred to cause a so-called "leak" in the light portions of the dye images.
The temporary shift of the dye developer can be generally attained by acylation of the auxchromic hydroxy or amino group of an azo dye. Since an azo dye can form two tautomers which are a hydrogen type with an absorption at comparatively longer wagelength side and an azo type with an absorption at shorter wavelength side, the temporary shift can be attained by acylation of the azo type tautomer.
A dye useful for desirable dye developer should satisfy the conditions that the absorption after the restoration is a desirable yellow color, that the absorption of the temporarily shifted dye is in a sufficiently shorter wavelength region so that the sensitivity of the emulsion is not affected thereby, that the restoration occurs rapidly due to the action of a processing solution, and that the restoration does not occur during the storage of the light-sensitive materials.
However, although conventional yellow azo dyes give preferred light absorption, conventional yellow azo dyes are insufficient as dyes for desirable dye developers, because, for example, pyrazolone azo dyes, 3-allylazo-2,4-dihydroxyquinoline and 2-allylazo-1,3-indanedion can not be acylated or can be acylated only with extreme difficulty; pyrazolobenzimidazole azo dyes and pyrimidazolone azo dyes can be acylated but the temporary shift is insufficient; or aniline type azo dyes can be acylated but the restoration can not be achieved by the processing solution.